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Abstract:
YbZnSn, YbAgSn, and Yb2Pt2Pb were synthesized by reacting the elements
in sealed tantalum tubes in a high-frequency furnace. The structures of
YbAgSn and Yb2Pt2Pb were refined from single crystal X-ray data: YbAgPb
type, P (6) over bar m2, a = 479.2(2) pm, c = 1087.3(3) pm, wR2 = 0.050,
BASF = 0.34(8), 509 F-2 values, 18 variables for YbAgSn and Er2Au2Sn
type, a = 776.0(1) pm, c = 701.8(2) pm, wR2 = 0.072, 426 F-2 values, 18
variables for Yb2Pt2Pb. The lattice constants of YbZnSn are confirmed:
NdPtSb type, P6(3)mc, a = 464.7(1) pm, c = 747.7(2) pm. The stannides
YbZnSn and YbAgSn crystallize with superstructures of the AlB2 type. The
zinc (silver) and tin atoms form ordered Zn3Sn3 and Ag3Sn3 hexagons,
respectively. The stacking sequences for the differently oriented
hexagons are AB, AB for YbZnSn and ABC, ABC for YbAgSn. While
exclusively Zn-Sn intralayer interactions were observed in YbZnSn,
intralayer Ag-Sn and significant Sn-Sn interlayer interactions at 318 pm
occur in YbAgSn. The [ZnSn] and [AgSn] polyanions in YbZnSn and YbAgSn,
respectively, have a pronounced two-dimensional character. This picture
of chemical bonding in YbAgSn is confirmed by TB-LMTO-ASA band structure
calculations. The partial densities-of-states and the valence charge
densities are discussed. The magnetic (no long-range ordering, Yb2+) and
the resistivity measurements (metallic behavior) are in excellent
agreement with the electronic structure calculations. Yb2Pt2Pb
crystallizes with the Er2Au2Sn structure, a ternary derivative of the
Zr3Al2 type. This structure is composed of distorted AlB2 and CsCl
related slabs of compositions YbPt2 and YbPb. Yb2Pt2Pb shows
paramagnetic behavior (4.3+/-0.4 mu(beta)/Yb) indicating trivalent
ytterbium. Magnetic susceptibility measurements on YbZnSn and YbAgSn
show Pauli paramagnetism with room temperature susceptibilities of
2.5(1) x 10(-9) and 4.6(1) x 10(-9) m(3)/mol. Electrical resistivity
measurements indicate metallic conductivity with specific resistivities
of 440 +/- 40 mu Omega cm (YbZnSn) and 490 +/- 40 mu Omega cm (YbAgSn)
at 300 K. Sn-119 Mossbauer spectra of YbZnSn show a single signal at
room temperature with an isomer shift of delta = 1.85(1) mm/s. YbAgSn
shows two superimposed signals at 78 K: a singlet at delta = 1.94(1)
mm/s and a second signal at delta = 1.99(1) mm/s subjected to quadrupole
splitting of Delta E-Q = 1.35(1) mm/s, in agreement with the two
crystallographically different tin sites. (C) 1999 Acamedic Press.
